Venus's volcanoes

The planet Venus has at least sixteen hundred major volcanoes and many more minor ones, which is more volcanoes than any other planet in the solar system. Most are shield volcanoes, but Venus also has pancake domes and other volcanic features. About 80 percent of Venus’s surface has been shaped by some type of volcanic activity. Venus does not have volcanic chains like those formed on Earth from plate tectonics. Comparing volcanic features on Venus and Earth helps scientists better understand volcanic processes on both planets.

Overview

Venus is sometimes referred to as Earth’s twin sister because its size, mass, and density are similar to those of Earth. Venus’s surface conditions, however, definitely make Venus Earth’s “evil” twin sister. Owing to a runaway greenhouse effect from the carbon dioxide atmosphere, Venus has a surface temperature hot enough to melt lead. The surface atmospheric pressure is nearly one hundred times what it is on Earth. Thick layers of sulfuric acid clouds veil the surface of Venus. Landers on Mars can last for years, but on Venus, they are destroyed by the harsh surface conditions within hours. These atmospheric conditions make it impossible to study the surface of Venus using direct optical means or long-term robotic landers. Astronomers must use radar maps rather than optical photographs to study the planet’s surface features. Radar maps from both Earth and spacecraft have, however, unveiled the surface of our mysterious twin sister.

Radar maps show that volcanic activity has played a major role in shaping the surface of Venus. Volcanic activity includes not only erupting volcanoes but also lava flows and other activity whereby solid, liquid, or gaseous material escapes from the planet’s interior. Volcanic activity is often caused by tectonic activity but can occur independently of tectonic activity. There are more than sixteen hundred large volcanic features on the surface of Venus and possibly as many as hundreds of thousands of smaller volcanic features. In addition, about 80 percent of the planet’s surface is covered with flat plains that are probably solidified lava flows. These lava plains formed when lava flooded areas covering thousands of square kilometers and then solidified.

Most of the volcanoes on Venus are shield volcanoes. Shield volcanoes derive their name from their resemblance to ancient warriors’ shields lying on the ground, pointing upward. Shield volcanoes are often very large, but they have fairly gentle, rather than very steep, slopes. Shield volcanoes form when lava flows out from a single central vent. Rather than forming on the boundaries of tectonic plates, shield volcanoes usually form over a volcanic hotspot. These hotspots are places in the planet’s crust where lava wells up from the planet’s mantle. When the lava breaks through the surface, it erupts to form a shield volcano. Successive eruptions can form very large shield volcanoes.

Two of the larger known shield volcanoes on Venus are Sif Mons and Gula Mons. They respectively have peak altitudes of about two and three kilometers above the surrounding surface, which compares to Mauna Kea, Earth’s largest shield volcano, which rises about nine to ten kilometers above the Pacific Ocean floor. (The largest shield volcano in the solar system is Mars’s Olympus Mons, which towers about twenty-five kilometers above the Martian surface.) Often, the top of a shield volcano will collapse to form a crater known as a caldera. This collapse occurs when the lava flow retreats back to the planet’s mantle, leaving nothing to support the top of the volcano. The calderas formed on Sif Mons and Gula Mons are about one hundred kilometers across. Calderas are fairly common on the surfaces of both Venus and Earth. Calderas, however, are not the only types of craters found on Venus. Venus has many large impact craters that formed from meteorite impacts rather than volcanic activity.

The largest volcanic features found on Venus are coronae. These features are not found on the other terrestrial planets. Coronae, which are approximately circular in shape (hence their name, from the Latin for crown), form from an uplifting process. Hot mantle material swells and pushes the crust upward. Coronae usually have associated volcanoes and lava flows. Aine is a large corona on Venus that is about three hundred kilometers in diameter. On a larger scale, Lakshmi Planum, which is part of Ishtar Terra—one of Venus’s two large continental-sized features—is about fifteen hundred kilometers at its widest point. Lakshmi Planum likely formed from the same process that formed the coronae but on a larger scale.

Another common type of volcano found on Venus is the lava dome or pancake dome. Venus’s lava domes are much smaller than its shield volcanoes, being typically tens of kilometers in diameter or less. They are usually circular and relatively flat—hence the name “pancake dome.” They form when lava slowly flows out onto the surface and then flows back. However, a thin crust solidifies on the surface of the lava. When the lava subsides, the crust stays and cracks because it lacks support. Pancake domes are often found near coronae.

On Earth, volcanoes often form at the boundaries of the tectonic plates. Examples are the volcanoes on the western coasts of North and South America and the Mid-Atlantic Ridge, which runs along the Atlantic Ocean’s floor between the North American and Eurasian plates. Such volcanoes are not found on Venus. Venus apparently does not have tectonic plates on its crust. Venus does not have plate tectonics similar to Earth’s, but it does have tectonic activity. On Earth, plate tectonics is caused by convection currents in Earth’s mantle slowly moving the crustal plates horizontally. On Venus, the crust is not divided into plates. Convection currents in the mantle cause vertical rather than horizontal crustal movement on Venus. Coronae are a good example of volcanic features formed on Venus from the crust’s vertical tectonic motion.

Are the volcanoes on Venus still active, as on Earth, or are they extinct, as on Mars? Planetary scientists do not yet definitively know the answer to this question. Despite being volcanically active, at any given time few of Earth’s many volcanoes are actively erupting. The same would be true on Venus. Hence, scientists would not expect to see volcanoes continually erupting on Venus, even if it is still volcanically active. Partly because of the planet’s thick cloud layer, no one has observed a volcanic eruption on Venus, but there is some indirect circumstantial evidence to suggest that volcanoes on Venus are still active. Volcanic eruptions emit sulfur dioxide gas. Scientists observe frequent variations in the amount of sulfur dioxide in Venus’s upper atmosphere. These variations could be caused by occasional volcanic eruptions spitting sulfur dioxide into the atmosphere. Space probes to Venus have also detected radio outbursts from Venus that are similar to those produced by lightning discharges from erupting volcanoes on Earth. These observations are evidence, but not proof, that Venus’s volcanoes are still active. If planetary scientists were to observe a volcano on Venus in the act of erupting, then Venus would join Earth and Jupiter’s satellite Io as the worlds in the solar system with still-active volcanoes. The European Space Agency's Venus Express, launched in 2006, and Japan's Akatsuki, launched in 2010, are collecting data regarding these atmospheric phenomena and aim to answer the volcanism question with certainty. Further, the Parker Solar Probe, as well as the Solar Orbiter, have also taken valuable pictures of Venus during fly-bys. In 2023, scientists gleaned potentially new data about Venus’s volcanoes by analyzing previously taken images by the Magellan spacecraft.

Knowledge Gained

Because thick clouds veil the surface of Venus, astronomers, for a long time, could only speculate about the planet’s surface. Prior to the space age, speculations varied: the surface was envisioned as hot and steamy by some, as a hot and dry desert by others. With the coming of the space age, astronomers were finally able to gather data on the surface of Venus. They did not, however, suspect just how hot Venus really was.

The first radar maps of Venus from Earth were made using the Arecibo Radio Telescope in Puerto Rico, beginning in the late 1970s. Because of the distance to the planet, these images had a relatively low resolution, on the order of a few kilometers. These Earth-based radar maps did, however, allow planetary scientists to observe the large-scale surface features of Venus.

Earth-based radar maps of Venus can reveal only part of the Venusian surface because, during Venus’s closest approach to Earth, only one side faces Earth. Orbiting spacecraft have therefore been sent to map the surface of Venus. Pioneer Venus 1 went into orbit around Venus in late 1978 and continued transmitting planetary data until 1992. This mission was the first orbital mission to use radar to map much of the surface of Venus, with a resolution of about seven kilometers. In 1990, the Magellan spacecraft went into orbit around Venus. During its four years in orbit, Magellan made much more extensive and detailed radar maps of Venus. Because it used a polar rather than an equatorial orbit, the Magellan orbiter was able to map essentially the entire surface, including the polar regions, which were hidden in previous missions. The best resolution of the Magellan radar maps is about hundred meters. Scientists continue to analyze the data from the Magellan.

The fact that Venus has volcanic activity, including both volcanic mountains and lava plains, indicates that geologically speaking, the surface of Venus is very young. The surface, not the planet itself, is probably less than a half billion years old.

Context

The volcanoes on Venus contribute to its very harsh surface environment. Volcanoes on Earth outgas significant amounts of carbon dioxide gas. Those on Venus and Mars probably do the same. On Earth, biological activity, such as plant respiration, uses carbon dioxide. Earth, therefore, has a very small percentage of carbon dioxide in its atmosphere. On Venus, however, the carbon dioxide is still in the atmosphere; 97 percent of Venus’s atmosphere is carbon dioxide. All this carbon dioxide produces a runaway greenhouse effect and surface temperatures greater than seven hundred kelvins.

Jupiter’s moon Io is also volcanically active. However, the volcanoes on Io differ from the volcanoes on Venus and other terrestrial planets. In addition to rock, Io’s composition includes significant amounts of ice.

Venus, Mars, and Earth all have large volcanoes. However, the volcanic and tectonic activity is different on each of these three planets. The differences arise from differences in size and internal heating of the planets. Mars has had the least amount of volcanic activity. Earth’s crust is divided into several tectonic plates. Movement of these plates is an important force in shaping the volcanic activity on Earth. Venus does not have a crust broken into several plates. Hence, Venus has much volcanic activity, but it does not have the types of features formed by crustal plate movement. Understanding how volcanic and tectonic activity differs among the various planets is one of the frontiers of planetary science.

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